Variant Creutzfeldt-Jakob disease and the risks from blood transfusion (page 2 of 4)
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The incidence of deaths in the UK peaked in 2000 with 28 deaths and has declined thereafter with only 5 deaths in 2005. The median age at death has remained stable at approximately 28 years, with a significant excess of cases in those aged 10 to 40 years. This excess is most likely to be due to increased susceptibility in the young, but could also be due to greater exposure. Host genetics also influence susceptibility, with all clinical cases to date having a genetic characteristic shared by approximately 40% of the population (methionine homozygous at codon 129 of the prion protein gene). Recent findings have shown that other genetic groups are also susceptible to infection2 but to date no clinical cases have been observed.
Transmission
The primary route of transmission of vCJD from cattle to humans is believed to occur through consumption of BSE-infected beef and beef products. Over the course of the BSE epidemic in Great Britain it is estimated that up to two million infected animals were slaughtered for human consumption. Whilst the majority of the population was therefore likely to have been exposed to the infectious agent, it is still uncertain to what extent the population is infected. Studies in mice and hamsters have demonstrated a substantial species barrier for these types of disease and hence it is likely that transmission from cattle-to-cattle is much more effective than from cattle-to human.
Recently, concern has arisen over the possibility of onward human-to-human transmission. High levels of the infectious prion agent are believed to aggregate in regions of the body including the brain, the central nervous system and lymphoreticular tissues. One theoretically possible source of transmission is via surgical instruments used on multiple patients which permit transmission because prions are able to withstand high temperatures and sterilisation methods. A second potential transmission route is via blood transfusion, which was demonstrated to be feasible in sheep studies.3 More recently, three vCJD infections have been identified in UK patients who received red blood cell transfusions using blood donated from individuals who later went on to develop vCJD.2,4,9 The first transmission occurred through blood donated from the index patient 3·5 years before onset of disease and resulted in the onset of clinical vCJD in the recipient 6·5 years after receiving the blood transfusion.4 The second transmission occurred through blood donated by the index patient 18 months before onset of disease.2 In this case, the recipient died from unrelated causes five years after receiving the blood transfusion, but at autopsy was found to have signs of vCJD infection in her spleen.
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